I used to use Kent when I had a reef years ago. Now I have IO. I just found a very interesting site with all of the info about what each mix contains. Go to http://www.advancedaquarist.com/2005/11/aafeature1 to read the full article. Another interesting part of the study was the yield of a 50 Gal bag standardized to a salinity of 35 ppt. Kent yielded 42.2 Gal, Aquamedic and Oceaniac 42.29 and 42.96 Gal while IO provided a yield of 45.13 Gal. Seems to me that this amounts to 5-7% more salt for the $$$’s than most other salts. Take a look at the heavy metals and such and let me know your thoughts. (I am lazy and have not had the time to study the report the way I should.:mrgreen: )